I believe that the "only a window cleaner" is something that is in our own self perception, and that perception derives from the lack of consideration many of our customers show us.
It's what we think they are thinking about us, not the way we think about ourselves.
We have all felt it at some time, a customer that owes for two months cleaning drives past you, making sure that you are invisible.
The cars in the drive, the tellys on, but there's no answer when you knock, 5 mins later the car has gone.
The windows that you pushed shut 10 mins ago are open again, but they don't answer the door.
You posted your cleaned the window slip saying collect on Thursday, Thursday comes and they got no money.
Customers of 10 years standing write out a cheque leaving your name blank. Guys I could go on, but you get the gist.
When people treat us like this, it's no wonder that "yeah, I'm only the window cleaner" feeling effects us.
We just get on with it, and smile when we count our pennies.